What does it mean?
P1651 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cooling Fan 1 Relay Control Circuit Malfunctions .
Symptoms
- MIL on and coolant temperature climbing at idle or in traffic while it stays normal at speed
- Fan never runs, or runs at full speed constantly, sometimes even with the ignition off
- A/C cooling drops off at idle and the module may disable the compressor
- Repeated fan fuse failures
- Coolant smell, steam or expansion tank overflow after slow-speed driving
Likely causes
- Cooling fan relay failed, or its contacts welded closed
- Burnt or loose terminals in the relay socket from the high fan current
- Open or shorted relay control wire between the module and the relay
- Blown fan fuse or fusible link
- Fan motor drawing excessive current or seized, which burns relays and sockets
- Corroded connector at the fan motor or a poor fan circuit ground
- Water in the underhood fuse box, or a failed low-side driver in the module
How to fix it
- Watch coolant temperature and the commanded fan state on live data, then command fan 1 on and off with the scan tool
- Check the fan fuse, then substitute an identical known-good relay and retest
- Back-probe the relay socket for battery feed, ground and the module control signal
- Check continuity from the relay socket to the module pin and test the control wire for shorts to ground and battery voltage
- Run the fan motor directly from a fused supply and measure its current draw; a motor above specification will kill the new relay too
- Repair or replace burnt relay socket terminals and clean the fan motor ground
- Replace the fan motor if it is seized or high-current, and only then look at the module driver